Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $88.43   8.157%   $95.6432   $95.64   $95.65   $95.60  
  Purchase #2 $48.51   5.729%   $51.2891   $51.29   $51.30   $51.30  
  Purchase #3 $80.50   8.438%   $87.2926   $87.29   $87.30   $87.30  
  Purchase #4 $235.70   7.746%   $253.9573   $253.96   $253.95   $254.00  
  Purchase #5 $159.81   4.177%   $166.4853   $166.49   $166.50   $166.50  
  Purchase #6 $53.54   4.403%   $55.8974   $55.90   $55.90   $55.90  
  Purchase #7 $52.61   7.513%   $56.5626   $56.56   $56.55   $56.60  
  7 purchase totals = $719.10       $767.1275   $767.13   $767.15   $767.20